.loading {
    .loading-css {
        width: 100px;
        height: 100px;
        background: blue;
        transition: width 2s;
        /* Firefox 4 */
        -moz-transition: width 2s;
        /* Safari and Chrome */
        -webkit-transition: width 2s;
        /* Opera */
        -o-transition: width 2s;

        &:hover {
            width: 400px;
        }
    }

    .loading-css-auto {
        width: 0px;
        height: 100px;
        background: red;
        transition: width 2s;
    }

    .loading-css-auto-hover {
        width: 400px;
    }

    @keyframes loading {
        from {
            width: 0;
        }
        to {
            width: 400px;
        }
    }
    .loading-animation {
        height: 100px;
        background: yellow;
        animation: loading 2s;
    }
    .loading-js {
        height: 100px;
        width: 10px;
        background: orange;
    }
}